1. Field of the Invention
The present invention relates to the provision of drinking water for animals, and more particularly to devices for maintaining a constant supply of water which remains: 1) free of debris or other contaminants during operation, 2) above the freezing temperature during the winter months, and 3) below the ambient air temperature during the summer months.
2. Brief Description of the Prior Art
For many years, owners of cattle and other livestock have sought an economical and practical solution to providing sources of fresh water to their herds during the winter months. Even today, water continues to play a central role in the diet of all healthy animals. Once the ambient air temperature drops below freezing, any source of water directly exposed to the elements begins to freeze. The consequences resulting from a frozen water source range from the mere nuisance of having to periodically attend to the source to the more catastrophic outcome of losing an entire herd in the event that another source cannot be provided for an extended period.
Since these consequences are well known to those in the art, many attempts to solve the related problems have been implemented. In milder climates that experience only an occasional period of subfreezing temperatures, insulated containers or electric heating elements provide an adequate solution. In harsher climates or in situations in which water supplies cannot be attended to as frequently, however, insulated containers alone eventually freeze over and providing sufficient heating through use of an electric element becomes prohibitively expensive.
Accordingly, various heat exchange devices have been designed to harness the naturally occurring potential which results because of the differential between the subfreezing air temperature and the constant temperature of the earth below the frostline. (In most colder climates in the United States, the frostline is between two to three feet below the surface of the earth.) At some distance below the earth's surface and below the frostline in the region, the temperature remains constant at approximately 54.degree. F., regardless of the ambient air temperature above ground. During periods of subfreezing air temperatures, this source of heat from below ground can be used to maintain a water supply at a temperature above freezing.
Numerous systems attempting to harness this subsurface heat have been disclosed. Some of these systems operate on a mechanically induced recirculation principle. In general, as disclosed in U.S. Pat. No. 3,221,706, issued to Johnson on Dec. 7, 1965 and entitled "Circulating Live-stock Watering System", these systems feature an underground pressurized water supply line that feeds into the bottom of a tank situated below the frost line. During operation, a float control system senses the level of the water within the tank and, if necessary, triggers the water supply line to begin feeding the tank. A continuously operating electric pump circulates water through a circuit. In the first portion of the circuit, water in the tank is first drawn upward through an inlet line and then enters a drinking basin disposed above the surface of the ground through a basin inlet. The basin inlet is disposed near the bottom of the basin. Water entering the basin agitates the residual pool of water there, thus slowing the freezing process. (Additionally, this agitation supposedly inhibits the growth of algae during the summer months.) If the level of the residual pool has fallen below a predetermined height, the entering water begins to fill the basin. Once the predetermined level is reached, however, the entering water flows out through the basin outlet and begins returning to the tank through via a return conduit, thereby completing the circuit. Consequently, water drawn from the pressurized supply line into the tank remains in circulation between the tank and the basin until the water is consumed or it evaporates.
Since the basin outlet is necessarily disposed at a height greater than the basin inlet, water in the basin could flow in a reverse direction and drain back into to the tank via the inlet line in the event of a pump failure. Because the basin inlet is disposed near the bottom of the basin, any sediment or other undesirable foreign matter in the basin would then be carried by the draining water into the tank, thereby increasing the likelihood of contamination. An attempt to address this drawback appeared in U.S. Pat. No. 3,306,263, issued to Johnson on Feb. 28, 1967 and entitled "Recirculating Live-stock Watering System". The Johnson '263 patent discloses a basin inlet disposed well above the basin outlet.
As disclosed in U.S. Pat. No. 4,584,966, issued to Moore on Aug. 29, 1986 and entitled "Livestock Watering System", the same recirculating system can be configured to supply relatively warmer water during the colder months and relatively colder water during the warmer months by using a selectively activated thermostatic control system. This system circulates water from the tank to the basin as the temperature of the residual pool either increases or decreases from a predetermined setting.
Instead of continuously circulating the water, other systems provide for supplying it upon demand. For example, as disclosed in U.S. Pat. No. 4,813,378, issued to Lapp on Mar. 21, 1989 and entitled "Animal Watering Fountain", an animal can actuate a lever in the basin which in turn opens a valve that then allows water to enter the basin. Any remaining water drains from the basin back into the underground tank.
By way of contrast to mechanically induced circulation systems described above, others operate on a natural convection principle. In these systems, e.g., as disclosed in U.S. Pat. No. 5,003,928, issued to Ketterlin on Apr. 2, 1991 and entitled "Freeze Resistant Animal Watering Installation", the top of the underground tank protrudes through the surface of the ground and serves as the drinking basin, while the bottom of the tank remains disposed below the frostline. Natural convection results by virtue of the temperature differential between the water at the top, which is relatively cooler because it is exposed to the air, and the water at the bottom of the tank, which is relatively warmer. Accordingly, water from the bottom of the tank rises to the top, cools, and returns to the bottom again in a cyclical fashion.
As shown in the prior art discussed above, e.g. U.S. Pat. No. 4,584,966, a reservoir can be disposed below the frostline, thereby preventing the water within it from freezing. Circumstances arise, however, in which the loss of heat from the drinking water supply above ground exceeds the amount of heat that can be transferred from the relatively warmer water in the reservoir disposed below ground on account of natural convection alone. In these situations, forced circulation provides additional heat transfer and further forestalls the freezing process. Even with the added forced circulation, however, the animals must often drink extremely cold water, i.e., water at a temperature just above the freezing point.
It would be advantageous to provide a system which would employ the principles of both induced circulation and natural convection to maintain the temperature of drinking water above freezing in the winter and below the ambient air temperature in the summer. Such a system would perform more effectively than one operating on either principle alone.
It would also be advantageous to provide a system which would provide greater assurances that the drinking water will remain free of debris and contamination during operation. In such a system, the drinking water which becomes subject to contamination after being exposed to the elements and animals is not recirculated for the purposes of transferring heat to the basin.